Electric beds have become more popular recently. The bed board of a common electric bed comprises multiple boards including: a head board, a fixed board, a leg board, and a foot board, which are sequentially connected together by a hinge, and lifted by a motor driving the bed board. The bed folds and moves to meet the requirements for user postural changes.
Nonetheless, the motor used generally for the electric bed is a linear actuator and its driving mode is simplest original direct driving mode, namely one of the push rod motor is hinged with the bed frame. Another end is hinged with the bed board. The push rod motor directly pushes the bed board and rotates around the hinge joint with the lifting of the bed board. When the push rod motor lifts with the bed board, the push rod continuously changes in direction and position so that the operating condition of the push rod motor is always in a changeable unstable status. In this unstable operating condition, it is possible to cause failure in the push rod motor and accident resulting in injury to the user during use of the electric bed.